A number of references show developing units which are movable into position with respect to an image member as part of the operation of the machine. For example, U.S. Pat. No. 4,928,146 shows apparatus in which four linearly arranged development stations are sequentially moved to a single development position to apply different color toner to four consecutive electrostatic images. U.S. Pat. No. 4,622,916 shows four toner stations on a rotary carriage which rotates the stations through a single development position to also apply different color toner to four consecutive images. U.S. Pat. No. 4,801,966 is typical of a large number of references showing toning stations that are movable in and out of their own unique developer position to apply the correct color toner to the image being toned. U.S. Pat. No. 4,891,672 shows a system in which one of a group of color stations is moved into a single toning position for a series of reproductions and then is replaced on demand from a storage position by another toning station of different color for another series of reproductions.
In most of these apparatus, a drum photoconductor is permanently fixed in the apparatus as is the supporting structure for each development unit. With such structure, critical positioning of each development unit with respect to the photoconductive drum can be managed by precise manufacturing and assembly of those parts and their supporting structure. It would be desirable to remove the need for such precision.
U.S Pat. Nos. 4,922,302 issued to Hill et al on May 1, 1990; 4,884,109 issued to Hill et al on Nov. 28, 1989 and 4,797,704 issued to Hill et al on Jan. 10, 1989; show a development station having an applicator with a rotating magnetic core and a stationary non-magnetic sleeve around which a developer mixture is moved by rotation of the core to pass the developer through a development position. The applicator is fed by a rotating paddle positioned below the applicator which both mixes developer and supplies it to the applicator. This particular structure requires that the applicator not be in contact with the image member carrying an electrostatic image to be developed, that it be precisely spaced from it.
In those structures in which a plurality of development stations can be alternatively positioned at a single development position with respect to a drum or other image member, precise positioning of the applicator of those development units is very challenging. In instances in which the applicator is positioned by a pair of rollers on either end of the applicator which mates with the image member, not only must the rollers be positioned and sized accurately, but the applicator must also be parallel to the axis of rotation of the image member. Further, if the applicator is flat on top as in the Hill et al disclosures above, the applicator itself must not be rotated about its axis or its separation from the photoconductor will be affected.
U.S. Pat. No. 4,699,494, Honda, issued Oct. 13, 1987 is typical of a number of references which show a cartridge including a photoconductive drum and a development station which is separately loadable into an image-forming apparatus. Suitable drives in the image-forming apparatus mate with comparable drives in the cartridge to both rotate the photoconductive drum and a development applicator. This structure has the advantage that the development applicator is positioned accurately with respect to the drum during manufacture of the cartridge. However, a cartridge is not ordinarily large enough to hold 3 or 4 toning stations for making multicolor images.